Russian prosecutors have launched criminal proceedings against a Luxembourg-based subsidiary of the oil company Yukos, on charges of fraud in the bankruptcy case involving the oil firm.

Prosecutors charge the management of Yukos Capital SARL with illegally extending up to $4.5 billion in loans to the firm's subsidiaries, including those abroad, during the bankruptcy process.

The prosecutors, in a statement, said they have raided the firm's offices, seized documents and are questioning employees.

A Moscow court declared Yukos bankrupt earlier this month. The firm was Russia's largest oil producer until Russian authorities effectively broke it up with a series of tax claims.

Former Yukos chief Mikhail Khodorkovsky is in a Siberian prison, serving an eight-year sentence for fraud and tax evasion. His supporters say the legal action against Yukos amounts to Kremlin retaliation for Khodorkovsky's support of opposition politicians. Russian authorities deny this.